Many industries, including the bottled water, semiconductor, and pharmaceutical industries, utilize water in various ways to manufacture products, clean and sanitize components, and/or to provide services. For many of the industrial uses of water, the water must repeatably meet stringent quality requirements. For example, being the most widely used ingredient in the manufacture of drugs, within the pharmaceutical industry, water must meet stringent quality requirements mandated by the Food and Drug Administration, whether the water is used for cleaning, sanitizing, or for drug manufacturing. It is typical for water pretreatment and final treatment systems, and in particular pharmaceutical water pretreatment and final treatment systems, to include a number of components, including for pretreatment: media filters for removal of suspended solids, water softeners for hardness and ammonia (if required) removal, carbon filters to dechlorinate the water, polishing water softeners for ammonia removal, and a reverse osmosis or distillation system for final treatment.
In order to ensure proper operation and overall service life of such systems and their various components, a number of factors must be considered. Two such factors are the removal of microbial control agents (dechlorination) and control of microbial bacterial growth (sanitization). In this regard, the removal of microbial control agents is often necessary for such systems because the water provided by the local municipality often contains microbial control agents, such as chlorine or chloramines, which are put into the water by the local municipality to control bacteria within the municipality's distribution network. Such microbial control agents can be detrimental to some water pretreatment and final treatment components. For example, such microbial control agents can cause premature failures of reverse osmosis membranes and can cause severe stress cracking and corrosion of austenitic stainless steel components.
In order to remove such microbial control agents, water pretreatment systems can utilize a number of methods, two of which are chemical injection and carbon filtration. Because chemical injection introduces a possibility of chemical contamination of the water being treated, carbon filtration is widely accepted as the preferred method in the pharmaceutical industry. Carbon filter dechlorination is accomplished by passing chlorinated water over a bed of activated carbon media contained within a pressure vessel generally constructed of fiberglass, lined carbon steel, or stainless steel. Typically the activated carbon media is a natural material manufactured from coal, wood, peat, or coconut shell, which when activated by steam or other means has a tremendous adsorption capability provided by its microscopic physical structure and large internal surface area. As chlorinated water passes over the activated carbon bed, chlorine adheres to the surface of the carbon granules and is removed from the water. Carbon filtration can also be an effective means for the breakdown of chloramines (a combination of chlorine and ammonia). However, although the carbon media will adsorb the chlorine, subsequent downstream processes must be considered to address ammonia removal.
While they are an effective means for dechlorination, carbon filters can create an optimum environment for microbial bacteria to prosper, which raises the second factor identified above, control of microbial bacterial growth, thereby requiring that the carbon filters be sanitized, at least periodically, in order to control microbial bacterial growth. Within the pharmaceutical industry, carbon filters are sanitized typically by heat or by the addition of a chemical disinfectant, with provisions for validation and monitoring the effectiveness of the sanitization process also being requirements. When chemical disinfectants are used, provisions must be made to remove the chemical disinfectants and to monitor such removal. Because of this, heat sanitization is generally regarded as the preferred method.
Heat sanitization is accomplished by either elevating the temperature of water flowing through the carbon bed of the carbon filter, via an external heating source and recirculating system, or by the injection of clean steam into the carbon filter directly. Heat sanitization is an effective method to control microbial bacteria because the elevated temperature prohibits the survival of microbial bacteria. However, with either approach, the carbon filter must be isolated from service during the sanitization process, and both approaches require subsequent backwashing and rinsing steps to flush out the dead bacteria from the system. Unless the system includes a redundant carbon filter (which doubles the sites where bacteria can grow and proliferate), the water pretreatment process must be suspended for the duration of the sanitization process. If a redundant carbon filter is utilized in the system, the redundant filter must be properly sized to handle the full service load of the pretreatment system, or sanitization must be scheduled during periods of low demand. Typically, such heat sanitization process includes the steps of: isolating the carbon filter from service, draining the carbon filter (for clean steam approach only), heating, holding that temperature for sanitization, cooling down, backwashing and rinsing, and return to service.